1. Field of the Invention
The present invention relates to a car-mounted antenna apparatus, for example, for AM broadcasting, FM broadcasting, TV broadcasting and radio telephones.
2. Related art of the Invention
In recent years, a car has been equipped with various kinds of radio devices such as a television set, a radio telephone and a navigation system as well as an AM/FM radio set and it is expected that this trend will continue as long as new types of radio apparatuses are devised with developments in information technology. Since there radio devices use different frequency bands and radio wave formats, it is necessary to provide a plurality of antennas therefor. As antennas, for example, rod antennas, V-type dipole antennas and loop antennas are used. Since it is necessary to provide an antenna for each of the radio apparatuses as mentioned above, the number of antennas mounted on a car increases as the number of radio devices mounted on the car increases. Conventionally, each of the antennas is designed to be suitable for its target radio wave so that it delivers the best performance for the frequency band it uses. With such antennas, the performance, such as the directional gain, degrades due to the influence of other antennas and members which are present in the vicinity. Consequently, it is necessary to dispose of a multiple number of antennas in a limited space such as a car in a manner such that as much distance as possible is kept therebetween in order to prevent interference with other members. Therefore, where and how to dispose the antennas is important.
However, in mounting antennas on a car, it is necessary to dispose the antennas so that a distance is kept therebetween as described above because conventional antennas are designed to be suitable for their target radio waves, so that a large space is necessary for mounting the antennas and it is cumbersome to decide where to dispose the antennas. In addition, the conventional antennas have disadvantages in easiness of handling and appearance such as feeder writing. That is, with the conventional antennas, a large space is necessary for disposing of a multiple number of antennas intensively or close to each other in a limited space such as a car because disposing of a multiple number of antennas intensively or close to each other degrades the performance of the antennas.
In addition, conventional antennas, which pick up radio waves from inside the car as well as radio waves from outside the car, face a problem that noises caused by the engine and the like become jamming waves to degrade the reception condition.